Terrestrial Palaeoecology and Global Change

162 Valentin A. Krassilov. Terrestrial Palaeoecology
melanges, flysch and island arc-type volcanics topped by shallow marine deposits. The
radiometric dates obtained for Xigase (Nicolas et al., 1981; Tapponier et al., 1981; Allegre
et al., 1984) and stratigraphically equivalent ophiolites indicate their mid-Cretaceous
age (Honegger et al., 1982; Thakur & Misra, 1984; Schärer et al., 1984). They
form a thick series of nappes emplaced upon the Tethys-Himalayas in the Late Cretaceous
and are overthrust by the Trans-Himalayan granitoid belt in the Eocene. The belt
extends over the Naga Hills to the Arakan Yoma Range in Burma and over the Andaman
– Nikobar ridge to joining the circum-Pacific girdle.
The crustal mosaic north of the Himalayas include the Lhasa, Quingtang, Songpan–Ganzi,
Yangtze and Qaidam blocks sutured by the (from north to south) Yarlung–
Zangbo, Banggonghu–Nujiang, Jinsajing, Longmenshan and Kunlun ophiolitic zones
(Zhang, 2000). The Zangbo (Tsangbo) ophiolites of Lhasa (Nicolas et al., 1981) seem
closely correlative with those of the Ladakh zone of Himalayas (Thakur & Misra,
1984; Pedersen et al., 2001) indicating a synchronous tectonic development while
ruling out the allegedly separate diachronous accretions. On the Tibetan side, the Donqiao
ophiolite north of Lhasa comprises a Jurassic magmatic assemblage emplaced
during the mid-Cretaceous (Girardeau, 1984). Thrust complexes of this age are typical
of the Tanglha and Kukushili shear belts further north. Granitization following the
emplacement of ophiolite nappes is likewise synchronous over the peri-Indian belts.
As a whole, the Mesozoic Tethys appears to consist of two arms with diachronous
tectonic developments. In the northern arm extending from the western Mediterranean
over the Lesser Caucasus to Tibet, the mid-Jurassic ophiolites are emplaced in the late
Neocomian to mid-Cretaceous. In the Taurian – Iranian – Afgano-Himalayan arm to the
south, the ophiolites of mid-Cretaceous age are emplaced in the Late Cretaceous, at
about the Campanian – Maastrichtian boundary. The end-Cretaceous to Eocene rethrusting
took place over both arms. The timing of tectonic events is roughly synchronized
with the circum-Pacific belt in the northern arm and with the peri-Atlantic belt in
the southern arm.
V.7. Tectonomagmatic phases
Chronological correlation of tectonomagmatic events in the major fold belts indicates
global pulses of tectonic activity as postulated by Stille (1924), Umbgrove (1947) and
other classical school geologists. Thus, the Late Jurassic/Berriasian, Hauterivian/Barremian,
Albian/Cenomanian, Campanian/Maastrichtian and Cretaceous/Tertiary tectonic
pulses are felt all over the circum-Pacific, peri-Atlantic and Tethys belts, with resonances
over cratonic areas. The Late Jurassic to Neocomian downfaulting of continental
margins was accompanied by rifting of the continental crust responsible for the world’s
largest basaltic provinces of eastern Brazil and central – eastern Asia (with volcanics up
to 600 m thick in the Kerulen Basin, Mongolia: Frikh-Har & Luchitskaya, 1983).